Jeremy Pigeon

Supercontinuum generation from 2 to 20 μm in GaAs pumped by picosecond CO 2 laser pulses

We report on the generation of supercontinuum radiation from 2 to 20 μm in a 67 mm long GaAs crystal pumped by a train of 3 ps CO2 laser pulses. Temporal measurements indicate that sub-picosecond pulse splitting is involved in the production of such wide-bandwidth radiation in GaAs. The results show that the observed spectral broadening is heavily influenced by four-wave mixing and stimulated Raman scattering.

Amplification of multi-gigawatt 3 ps pulses in an atmospheric CO2 laser using ac Stark effect.

The 3 ps pulses are amplified to ~20 GW peak power in a TEA CO(2) laser using ac Stark broadening. Demonstration of such broadband coherent amplification of 10 μm pulses opens opportunities for a powerful mid-IR source at a high-repetition rate.

High-power, mid-infrared, picosecond pulses generated by compression of a CO_2 laser beat-wave in GaAs

We report on the generation of a train of ∼2  ps, 10 μm laser pulses via multiple four-wave mixing and compression of an infrared laser beat-wave propagating in the negative group velocity dispersion region of bulk GaAs and a combination of GaAs and NaCl crystals. The use of a 200 ps, 106 GHz beat-wave, produced by combining laser pulses amplified on the 10P(20) and 10P(16) transition of a CO₂ laser, provides a novel method for generating high-power, picosecond, mid-IR laser pulses at a high repetition rate. By using 165 and 882 GHz beat-waves, we show that cascaded phase-mismatched difference frequency generation plays a significant role in the four-wave mixing process in GaAs.

Measurements of the nonlinear refractive index of air, N 2 , and O 2 at 10 μm using four-wave mixing

We report on measurements of the nonlinear index of refraction of air, N2, and O2 at a wavelength close to 10 μm by collinear four-wave mixing of a 200 MW CO2 laser beat-wave. The use of a 200 ps long beat-wave comprising radiation amplified on the 10P20 and 10R16 lines of the CO2 laser provides a sensitive method to measure the small nonlinearities characteristic of the gas phase in a spectral region where no such data exists.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring

We have used multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, v_{HB}, of the density cavity pushed forward by a train of CO_{2} laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the v_{HB} falls rapidly as the laser pulse intensity falls at the back of the laser pulse train. A heuristic theory is presented that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. The measured values of v_{HB}, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.

High throughput on-chip analysis of high-energy charged particle tracks using lensfree imaging

We demonstrate a high-throughput charged particle analysis platform, which is based on lensfree on-chip microscopy for rapid ion track analysis using allyl diglycol carbonate, i.e., CR-39 plastic polymer as the sensing medium. By adopting a wide-area opto-electronic image sensor together with a source-shifting based pixel super-resolution technique, a large CR-39 sample volume (i.e., 4 cm × 4 cm × 0.1 cm) can be imaged in less than 1 min using a compact lensfree on-chip microscope, which detects partially coherent in-line holograms of the ion tracks recorded within the CR-39 detector. After the image capture, using highly parallelized reconstruction and ion track analysis algorithms running on graphics processing units, we reconstruct and analyze the entire volume of a CR-39 detector within ∼1.5 min. This significant reduction in the entire imaging and ion track analysis time not only increases our throughput but also allows us to perform time-resolved analysis of the etching process to monitor and optimize the growth of ion tracks during etching. This computational lensfree imaging platform can provide a much higher throughput and more cost-effective alternative to traditional lens-based scanning optical microscopes for ion track analysis using CR-39 and other passive high energy particle detectors.

Long-wave infrared picosecond parametric amplifier based on Raman shifter technology

A new method for a long-wave infrared (LWIR), picosecond difference frequency generation (DFG) source using one near-infrared laser and a Raman shifter is experimentally tested and characterized. The signal seed for DFG is a Stokes pulse generated via transient stimulated Raman scattering in a nonlinear medium with a Raman frequency in the 2-20 µm range. A study of the dynamics of the transient Raman regime in liquid C6D6 has shown that the efficiency of Stokes production can be increased and the central wavelength can be controlled by chirping the pump pulse in order to compensate for chirping caused by self-phase modulation. High energy, ≥3 µJ, picosecond pulses at 10.6 µm have been generated in a GaSe crystal pumped by 1 mJ pulses of 1060 nm light from a Nd:glass laser.

Nonlinear optical compression of high-power 10-µm CO2 laser pulses in gases and semiconductors

We review a series of experiments on nonlinear optical compression of high-power, picosecond, 10-µm CO2 laser pulses. Presented schemes include self-phase modulation in a Xe-filled hollow glass waveguide, self-phase modulation in GaAs followed by compression, and multiple four-wave mixing compression of a laser beat-wave in GaAs. The novel nonlinear optics and technical challenges uncovered through these experiments are discussed.

Four-wave mixing in the range of 9–11 μm in argon and air pumped by high-power CO 2 laser pulses

We report on four-wave mixing of a 0.5 GW, CO 2 laser beat-wave (10.27+10.59 μm) in air and argon. Sidebands from 9.7–11.3 μm were observed using 1 GW/cm2 laser intensities in a gas-filled cell.

Generation of broadband 10 μm pulses using four-wave mixing compression in GaAs

We report the generation of <2 ps 10 µm pulses by four-wave mixing compression of a 200 ps CO2 laser beat-wave in GaAs. Experiments reveal that phase-mismatched quadratic interactions contribute to the effective third-order nonlinearity.